Sound translating device



[July 12, 1938. wARNKE 2,123,640 v I scum) TRANSLATINGVDEVICE FiledApril 28, 1934 I: n C r r Patented July 12,- 1938 UNITED STATES SOUNDTRANSLATING DEVICE Herbert R. Warnke, Camden, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application April 28,1934, Serial No. 722,821

4 Claims.

My'invention relates to sound translating devices, and more particularlyto loudspeakers of the movable coil or dynamic type having a permanentmagnet field and a conical diaphragm.

In permanent'magnet dynamic speaker design with which I amfamiliar,large permanent magnet field yokes usually comprising a multiplicity ofbars have often been employed. The yokes and other parts of the speakerincluding the center and outer pole pieces are usually held together bybolts or rivets, and these structures have lacked desirable compactnessand magnetic efiiciency relative to bulk. Furthermore, as it isnecessary that certain parts of the speaker be critically positionedrelative to each other, it has been necessary that the holes for thebolts 01' rivets which hold the speaker together be very accuratelylocated. This, of course, is objectionable from a manufacturingstandpoint as it adds to the cost of and retards speed of production.

Also, welding has been used in assembling certain of the speaker parts.However, there are certain disadvantages in this method, namely, thestructures must be subjected to heat which often causes warping and themisalignment of the parts, and forms must be employed to hold thevarious parts in position during the operations.

It is, accordingly, the primary object of my in-v vention to provide apermanent magnet dynamic type loudspeaker and method of assemblytherefor which will be free from the defects and disadvantages of theprior art as noted in the foregoing.

A further object of my invention is to provide a permanent magnetdynamic type loudspeaker of high magnetic efliciency relative to bulkand of a substantially small dimension from front to back and,

A still'further object of my invention is to provide for a permanentmagnet dynamic type loud speaker, a method of assembly for the sev' eralparts which is adaptable to speedy production yet which insures extremeaccuracy in locating the parts relative to each other.

In accordance with my invention, I provide a dynamic type loudspeakerhaving permanent magnet field structure comprising one or more permanentU -shaped magnets.

In the structure. including one magnet, the ends or poles of the magnetare held in contact respectively with the top end of a soft iron plateconstituting an outer pole piece substantially the width of the magnetand the top end of a second soft iron plate which is disposed to the'rear of the first plate and is spaced therefrom by a nonmagneticspacing member. Fixed to the rear plate is a soft ironcylindrical centerpole piece which extends'for'ward and into a circular open.- ing in thefront plate to provide an air gap for 5 the movable coil of a cone typediaphragm. To insure accurate location-of the center pole piece in theopening in the front plate, I have devised a method of assembly wherebysuch accuracy is obtained although liberal tolerances may be allowedinthe location of holes and studs therefor which hold the partstogether.

In the embodiment of my invention which includes a plurality of U-shapedpermanent magnets, the front and back plates are modified to providecontacting surfaces for the respective poles of the magnets.

Welded to the front plate is a forwardly extending housingorrframeincluding a flange to which the rim of a cone diaphragm is attached. Anopening substantially the width and thickness of a pole of the Ll-shaped magnet is provided in'the housing through which the poleextends. The opening serves to prevent horizontal displacement of themagnet relatlveto the ends of the front and back plates. and a singlescrew passes through the top of the magnet, extends'downward and isthreaded into the spacing member to prevent vertical displacement.

The novel features which I consider character- 30 istic of my inventionare set forth with particularity'in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be un- 35 derstood from the following description of specificembodiments, when read in connection with the accompanying drawing, inwhich,

Figure l is a view in perspective of a permanent magnet dynamic typeloudspeaker con- 40 structed in accordance with my invention andemploying a single U-shaped permanent magnet.

Fig.2 is a vertical sectional View of a loudspeaker wherein thestructure shown in Figure 1 has been modified to employ a plurality ofpermanent U-shaped magnets.

Fig. 3 is a view partly in section and looking in the direction of thearrows on the line'33 of Fig. 2. V 50 Fig. 4 is a rear view of the backplate employed in the structure shown in Fig. 2.

Fig. 5 is a view in section illustrating a method of assembly forcertain parts of my improved loudspeaker.

Fig. 6 is a sectional view taken on the line B6 of Fig. 5.

Fig. '7 is a fragmentary sectional View further illustrating the methodof assembly; and.

Fig. 8 is an end view of a spacing member.

Referring, now, to the drawing wherein like numerals refer to like partsthroughout, there is shown in Fig. l a dynamic type loudspeakerincluding permanent magnet field structure constructed in accordancewith one embodiment of my invention.

A frustro-conical diaphragm I is mounted within a housing 3 and integralwith the housing is a circular flange 5 to which the rim of thediaphragm is secured in any suitable manner. The housing 3, which isconstructed of a light nonmagnetic metal such as aluminum, isconstituted by an open frame-work in order to further reduce weight andincludes top and bottom portions 1 and 9, respectively, extendingrearwardly of the flange. Back strips II and I2 are integral with thetop and bottom portions I and 9, respectively, and serve as places ofattachment for an assembly of the speaker parts which will now bedescribed. I

The above notedassembly comprises a plate l3 which functions as an outerpole piece, a back plate I5, a center pole piece I'I fixed to the backplate I5, and a non-magnetic spacing member I9 interposed between thetwo plates. upon the assembly with its two poles held in contactrespectively with the top ends of the front and back plates I3 and I5 isa permanent 'U-shaped magnet 2I.' The magnet 2| may be made of cobaltsteel to provide a maximum degree'of magnetic efiiciency. However, ascobalt steel is relatively expensive, in order to reduce manufacturingcost, I prefer to use chrmium steel, which is comparatively inexpensiveand entirely satisfactory. The front plate I3, the back plate I5, andthe center pole piece I! are preferably constructed of soft iron toprovide maximum magnetic permeability. As heretofore noted, the spacingmember I9 is made of a nonmagnetic material, such as a zinc alloy, forexample. Thus, the magnetic flux is confined as nearly as possible tothe proper path which is, of course, between the outer and center polepieces. I

"The front plate I3, which is substantially rectangular in shape and thewidth of the permanent U-shaped magnet'ZI, has its top end bent over tothe front at right angles to provide a surface of sufiicient area. foroverall contact with an end or pole; of the U-shaped magnet 2|. Formedin the front plate I3 is a circular opening 23 of sufiicient size toallow the entrance of a voice coil 25.

Extending into and centered in the opening 23 in the front plate I3isthe center pole piece I! which is of a smaller diameter than theopening. The space thus provided betwenthe center pole piece I1 and theWalls of the opening in the front plate I3 provides an air gap for thevoice coil 25. It will be observed from the drawing that the center polepiece I? is of a reduced diameter at the rear of the air gap and thatthe opening in the front plate I3 is countersunk. This acts to confinethe magnetic flux as nearly as possible across the air gap between thecenter and outer poles. A reduced cylindrical extension 21 terminatesthe center pole piece II at the rear and a hole is provided in the rearplate I into which the reduced extension 21 fits with its end flat-Mounted tened or riveted over to securely fix it to the plate.

The top of the back plate I5 is of substantially the same width andthickness as that of the pole of the U-shaped magnet 2| which is held incontact therewith. From the top downward, the plate I5 is of a graduallydiminished width and is the shape of an inverted isosceles triangle,having its apex cut off even with the bottom edge of the center polepiece I1. The diminution in the width of the back plate I5 is such thatits side edges are tangent with the periphery of the rear face of thecenter pole piece II. This reduces the amount ofsurface of the backplate which extends beyond the limits of the center pole piece, thusreducing flux loss between the front and back plates.

Referring now to Fig. 2, it will be seen that I may include a pluralityof permanent magnets in my improved loudspeaker, thus increasing itsmagnetic efiiciency. In this arrangement, it will be seen that the frontplate Hat and back plate I5a extend downward and terminate in endssimilar to their upper ends and so provide faces against which therespective ends of a second U-shaped magnet 2 la are held in contact.

In Fig. 4, it will be noted that the back plate I5a is of a reducedwidth at the center where the center pole piece I I is secured and thatit flares outwardly'toward the top and bottom to a width substantiallythat of the magnets.

From the above, it will be apparent that the plates I3 and I5 may bestill further modified to accommodate more than two magnets. Forexample, extensions similar to those provided at the bottoms of theplates in Fig. 2 may be provided at their sides. No illustration of thisis thought to be necessary, as it is apparent that the structures at thesides of the plates would be a duplication of those at the tops andbottoms.

Interposed between the front plate I3 and the back plate I5 and spacedfrom and located above the center pole piece I1, in the structure shownin Fig. 1, is the non-magnetic spacing member I9 which serves to holdthe plates including the center pole piece in proper relationship. Theends of the spacing memberl9'abut the inside faces of the platesrespectively and are accurately positioned and positively held in placein a novel manner to be presently described.

In order that the back and front plates I3 and. I5'may be securelymaintained in their relative positions after assembly and the centerpole piece thus centered in the opening in the front plate, it isdesirable to locate the spacing member I9 as near to the center polepiece as possible. Also, the ends of the spacing member must havesufficient contact area with the inside faces of the plates. In order toaccomplish this, the under side 29 of the spacing member I9 issubstantially semi-cylindrical in shape, as shown in Fig. l, and islocated so that it is spaced slightly away from and encirclessubstantially the upper half of the center pole piece I'I. 'At itsbottom, the spacing member I9 extends laterally on either side of thecenter pole piece I1 to a width substantially that of the front plateI3, and at its top, it is substantially the width of the back plate I5.As will be seen from the drawing, this construction provides the spacingmember with ample contact surface at the ends which abut the insidefaces of the plates. Furthermore,it permits the member l9 to be locatedin a position Where it most easily maintains the front and back platesin their relative positions and thus the center pole piece properlycentered in the opening in the front plate.

The method of assembling the front plate l3, back plate [5, center polel1 and the spacing member l3 will now be described with reference toFigs. 5, 6, '7 and 8 of the drawing.

As previously noted, the rear extension 21 of the center pole piece ITis fitted into a hole in the'back plate l and its end riveted over tofirmly afiix it theretc.- This is the first step in the assembly of theabove mentioned parts. Studs 31 on one end and studs 33 on the oppositeend are integral with the spacing member. The studs are fitted into,holes provided in the front and back plates respectively and are rivetedover, thus securing and locating the plates and center pole piece intheir proper relationship to each other. It will, of course, beunderstood that the end of the center pole piece I! must be veryaccurately located in the opening 23 in the front plate l3 to providethe air gap for the voice coil 25 which is located therein. It will bereadily appreciated that if the studs 3i and 33 are positioned in theirholes in the conveni tional manner, the holes, as well as the studs,

must be very accurately located. This is not adaptable to high speedproduction and entails expensive operations.

To avoidthe above noted disadvantages, I provide what I believe to be anovel method of assembly for the parts referred to, wherein liberaltolerances in drifting the holes and in locating the studs may beallowed.

The studs 35, located upon the end of the spacing member it which abutsthe front plate l 3, are of conventional design as will be noted from aninspection of Fig. 6. The location of the studs in the holes in thefront plate l3 and the riveting over of their ends constitutes thesecond step in my method of assembly and is performed in the usualmanner.

In accordance with my invention, the location of the center pole piecell, relative to the back plate l5, and the spacing member l9 relative tothe front plate 53, need not be achieved with any great degree ofaccuracy. However, the third step in my method of assembly, which isconstituted by the affixation of the back plate Hi to the spacing memberl9. and consequently the positioning of the center pole piece ll in theopening in the front plate 53, must accurately locate the center polepiece as has been previously noted.

The third assembly step will now be described, reference being had toFig. 8 of the drawing, which is a view of the end of the spacing memberit which abuts the back plate l5. It will be seen that the studs 33 havebase portions 35 which are hexagonal in shape and about the i height ofa conventional nut of the same dimensions, as will be more clearly seenin Fig. 6. At the base of the studs and extending under the corners ofthe hexagonal portions are circular grooves 3'! in the spacing members19.

The holes in the back plate [5 for the studs 33 are of a slightly largerdiameter than the cylindrical portions of the studs but smaller than thehexagonal portions 35. Although I have found it convenient to make thebase portions hexagonal, they may, of course, be made in other shapes.

In Fig. 5 is shown a form 39 with speaker parts which are to beassembled positioned thereon. The form 39 comprises a block 4i havingintegral therewith an upstanding cylindrical portion 43 and acylindrical well 45 at the bottomthereof and extending within the block.

The cylinder 43 has an outer diameter that will permit the front plateI3 tobe placed face downward upon the form with the cylinder fittingsnugly within the opening 23 in the plate, as will be noted in Fig. 5.The inner diameter of the cylinder 43, as also will be noted, allows thecenter pole piece H to be fitted snugly therein. From the above, it willbe seen that the thickness of the cylinder wall is substantially equalto the width of the air gap which is provided for the voice coil 25 inthe assembled loudspeaker.

Considering the assembled front plate l3 and spacing member. I9 as aunit and the assembled back plate l5 and center pole piece I? as anotherunit, the assembly of these parts will now be described. I

The front plate. 13, with the spacing member l9 uppermost, is placedupon the form 39 with the cylindrical portion 43 of the form extendingup-' wardly through the opening 23 in the front plate. Next the centerpole piece I! is fitted within the cylinder 43, the cylindrical ends ofthe studs 33 on the spacing member l9 are allowed to enter the holesprovided for them in the back plate l5, and the pole piece I! isextended into the well 45 provided in the form 39 therefor. Asillustrated in Figs. 5 and 6, it will be seen that the center pole piecei! will only be allowed to enter the cylinder 43 to a point where theback plate will rest upon the hexagonal portions 35 of the studs 33 asthe dimension of the hexagonal bases across their corners is greaterthan the diameter of the holes in the plate.

From an inspection of Figs. 6 and 7, it will be seen that application ofsuificient pressure upon the back plate I5 will cause the edges of theholes in the plate to cut or shave off the corners of the hexagonalbasis 35 of the studs and thus form for themselves new tightly fittingstuds constituted by the mutilated hexagonal bases. A conventional pressor the like (not shown) is utilized to exert pressure upon the backplate until its under;

face is flush with the adjacent end of the spacing member, and in sodoing, the holes in the plate are caused to act upon the hexagonal basesof the studs in the manner described above. It is, of course, obviousthat the material from which the studs and spacing member areconstructed is softer than the back plate.

In order to prevent the shaved off fragments of the hexagonal bases 35of the studs 33 from becoming wedged between the plate l5 and thespacing member I9, and so preventing them from being completely pressedtogether, the circular wells 3! in the spacing member at the base of thestuds are provided to receive the shavings.

In Fig. 6, it will .be noted that the studs 33 are not in exactalignment with the holes in the back plate 15. However, from theforegoing, it will be seen that, in spite of the misalignment of theparts, the center pole piece ll is accurately located within the opening23 in the front plate I3 to provide an air gap for the voice coil 25.

At the completion of the above described operation, the ends of thestuds 33 are flattened or riveted over, and removal of the assembly fromthe form 39 completes the operation.

In connection with the structure shown in Fig. 2, wherein two U-shapedmagnets are employed, it will be noted that a second spacing member l9ais utilized to further strengthen the union between the back and frontplates [3a and l5a, re-' spectively. The second spacing member [9a islocated relatively in the same relationship below the center pole pieceIT as the first spacing member I9 is located above, is substantially of.the same construction, and is secured to the front plate 13a and backplate Ia in the same manner. The same method of assembly as described inconnection with the structure shown in Fig. 1 is followed throughout,and it will be obvious that the assembly form 39 need only be slightlymodified to accommodate the bent over bottom end of the front plate l3a.

Upon the completion of the assembly operations described above, thesurfaces of the back plate I5 and front plate l3 upon which the ends ofthe U-shaped magnet 2| are to be located are ground to insure uniformcontact therewith. The assembly is then attached to the diaphragm conehousing 3 by welding the front plate [3 to the back strips H and I2thereof,'as will be seen in Fig. 1.

Provided in the top of the cone housing 3 is the opening 41 which servesto locate the U- shaped magnet 2| in proper relation to the front andrear plates l3 and I5, as is clearly shown in Fig. 3. The magnet 2| isplaced in position upon the front and back plates with a pole extendingthrough the opening 41 and a screw 49, passed through a hole in its top,extends downward and is threaded into the spacing member I9. It will beobserved that the opening in the cone housing prevents horizontaldisplacement of the magnet and the screw prevents vertical dislodgement.

It will be noted in Fig. 1 that I have utilized the bottom portion 9 ofthe cone housing for mounting an audio transformer or the like. However,in the construction shown in Fig. 2 the bottom 9a of the housing 3a isconstructed substan tially like the top portion la thereof and thesecond U-shaped magnet Zia is located and retained in position by theopening 41a and the screw 49a threaded into the second spacing member[9a. From the foregoing, it will be seen that I have provided apermanent magnet dynamic type loudspeaker of exceptionally compactdesign. Furthermore, the permanent magnet structure has been positionedrelative to the diaphragm so as to make the unit as shallow as possiblewithout the sacrifice of magnetic efiiciency. Such characteristics in aloudspeaker make it particularly adaptable to use in an automobileradio, for example. 7

Although I have used both riveting and welding in assembling myloudspeaker, it will be noted that the riveting operations are adaptableto high speed production without the sacrifice of accuracy and are freefrom the disadvantages of the prior art. Furthermore, the points of thestructure which are subjected to Welding are located where any warpingcaused by heat cannot affect the parts which must beaccuratelypositioned.

Although I have shown and described specific embodiments of myinvention, I am fully aware that many modifications thereof arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

1. In a loudspeaker including permanent magnet field structure and avoice coil, the combination of a plate comprising an outer pole pieceand having an opening therein, a second plate of magnetic materialspaced from said first named plate, a center pole piece attached to saidsecond named plate and extending into said opening in said first namedplate whereby an air ap for said voice coil is provided, andnon-magnetic means spacing said plates from each other and maintaining,said plates in such relation as to provide said air gap.

2. In a dynamic type loud speaker, the combination of a plate comprisingan outer pole piece, a second plate spaced from said first named plate,non-magnetic means maintaining said plates in spaced relation, a centerpole piece attached to said second named plate, and a permanent magnethaving its poles respectively in contact with portions of said first andsecond named plates, said magnet being so disposed with respect to oneof said plates as to have at least a portion thereof in the plane ofsaid latter plate. 3. In a loudspeaker including a diaphragm and a voicecoil, the combination of a housing for said diaphragm having a pluralityof openings therein, a plate comprising an outer pole piece having anopening therein and attached to the back of said housing, said platehaving an end thereof bent over and extending into said housing throughone of said openings therein, a second plate disposed to the rear ofsaid first named plate, a non-magnetic spacing member interposed betweenand having its ends respectively attached to the inner faces of saidfirst and second named plates, a center pole piece attached to saidsecond named plate and extending forward into said opening in said firstnamed plate whereby an air gap is formed for said voice coil, andpermanent magnet structure having a pole thereof extending through oneof said openings in said housing and contacting With the bent overportion of said first named plate and having its other pole contactingwith an end of said second named plate.

4. The invention as set forth in claim 3 characterized in that saidmagnet structure comprises a plurality of permanent magnets each havinga pole thereof extending through one of said openings in said housingand contacting with an end portion of said first named plate and havingthe other pole thereof contacting with one end of said second namedplate.

HERBERT R. WARNKE.

